The present invention relates to an aluminum alloy heat exchanger resistive to tobacco odor impregnation, absorption and sticking. In particular, the present invention relates to an aluminum alloy heat exchanger with a coating having a reduced absorption of the odorous components of tobacco, etc.
When an aluminum alloy heat exchanger usable as an air conditioner for a motor car is operated, condensed water adheres to the surfaces of fins. When the fin surfaces have a low wetting property, the condensed water forms water droplets substantially in the form of semispheres on the fin surfaces, or water bridges are formed between the fin surfaces. The semispheric water drops and the water bridges form resistance to airflow and other problems, for example, a reduction in heat exchange efficiency and generation of noise. In the prior art for solving the above-mentioned disadvantages, an organic hydrophilic coating is usually formed on the surface of the heat exchanger. For example, Japanese Unexamined Patent Publication No. 1-299,877 discloses a coating formed from a combination of polyvinyl alcohol with a specific water-soluble polymer and a cross-linking agent, Japanese Unexamined Patent Publication No. 1-270,977 discloses use of polyacrylamide resins, Japanese Unexamined Patent Publication No. 6-306,247 discloses copolymerization of specific hydrophilic monomers, and Japanese Patent No. 2520308 (JP-A-2-258874) discloses use of organic hydrophilic treating agents comprising carboxymethylcellulose polymers, N-methylolacrylamide, polyacrylic acid and a zirconium compound.
It is also known that odorous components contained in the ambient atmospheric air or air contained in the heat exchanger are absorbed by the condensed water adhered to the surface of the heat exchanger and are gradually accumulated on the heat exchanger surface over time, and then the odorous components are released from the heat exchanger surface during operation of the air conditioner, and give off an offensive odor.
As a method for deodorizing the heat exchanger, it is well known to employ activated carbon. In this method, the activated carbon is shaped into pellets or a honeycomb, and the odorous components in air are absorbed in fine pores formed in the surface portions of the shaped activated carbon by diffusion or circulation or ventilation of the odorous component-carrying air through the heat exchanger.
In other deodorizing methods not using the absorption procedure, the absorbing material is reactivated by an electric heating procedure. In this method, an absorbing material and a noble metal oxide catalyst are carried on a surface of a heating resistor, while the absorbing material has a satisfactory absorbing activity, the absorbing material is used for deodorizing purposes at room temperature, and when the absorbing activity of the absorbing material becomes insufficient, the heating resistor is electrically activated to heat the absorbing material to a temperature of 300xc2x0 C. or more, and to oxidatively decompose the odorous components absorbed in the absorbing material, and to reactivate the absorbing material.
Also, as a technology for activating a heat exchanger surface, Japanese Unexamined Patent Publication No. 8-296,992 discloses a heat exchanger utilizing a photocatalyst. In this heat exchanger, a mixture of a photocatalyst with a binder is coated on the surfaces of heat exchanging aluminum fins, an ultraviolet ray lamp is arranged so that ultraviolet rays can be irradiated toward the heat exchanger. When the photocatalyst-containing coating is irradiated by the ultraviolet rays, the adhesion and accumulation of the odorous components on the heat exchanger surface can be reduced.
Among the above-mentioned deodorizing methods, the methods using the absorption activity have the following problems. When activated carbon is used, the deodorizing activity of the activated carbon decreases with an increase in the amount of the absorbed odorous components, with the activated carbon finally being saturated by the absorbed odorous components and ceasing to have a deodorizing activity. Sometimes, activated carbon saturated by the odorous component itself becomes a source of generation of the offensive odor. Also, when the deodorizing material is placed in an air conditioner in practice, the space velocity is too high, and thus the time of contact of the odorous component-containing gas with the deodorizing material is insufficient, the degree of deodorization of the deodorizing material per pass of the odorous component-containing gas is low, and thus the resultant deodorization effect is insufficient. To improve the above-mentioned method, it is necessary to decrease the space velocity and to increase the deodorizing activity. However, to satisfy this requirement, the absorbing material and a certain carrier for the absorbing material must be formed into a large-scale honeycomb, and this causes the cost of the absorbing material to increase.
In the deodorizing method in which the absorbing material is reactivated by electrical heating, replacement of the absorbing material is not necessary. However, for the purpose of reactivation, the absorbing material must be heated to a temperature of about 300xc2x0 C. or more, which may cause the absorbing material to be unnecessarily heated to a high temperature and the environs of the absorbing material to become dangerous.
When the photocatalyst as disclosed in Japanese Unexamined Patent Publication No. 8-296,992 is employed, the necessary ultraviolet ray lamps cause the method cost to increase, and a new problem in that intermediate decomposition products of the odorous components produced in the presence of the photocatalyst may be a source of offensive odor.
An object of the present invention is to provide an aluminum alloy heat exchanger resistive to impregnation, absorption and sticking of tobacco odor or other odorous components, to solve the above-mentioned problems of the prior art.
The inventors of the present invention conducted extensive research in order to find solutions for the above-mentioned problems and, as a result, found that the amount of an odorous component such as tobacco odor absorbed in the surface of a heat exchanger can be significantly reduced by coating the surface of the heat exchanger with a coating layer comprising (A) at least one chitosan compound selected from chitosan and derivatives thereof and (B) at least one carboxylic compound having at least two carboxyl groups per molecule of the compound, the total solid amount (A)+(B) of the chitosan compound component (A) and the carboxylic component (B) being 20% by mass, based on the total amount by mass of the coating layer. Also, it was found by the inventors of the present invention that the hydroplicity of the organic hydrophilic coating layer and the prevention property for absorption of the odorous component by the organic hydrophilic coating layer can be further enhanced by adding a hydrophilic polymeric substance different from the chitosan compound (A) and the carboxylic compound (B), as a component (C) into the organic hydrophilic coating layer, a solid content in the range of from 0.1 to 10% by mass. The present invention has been completed on the basis of the above-mentioned findings.
The aluminum alloy heat exchanger of the present invention resistive to tobacco odor impregnation, comprises a base body of aluminum alloy heat exchanger and an organic hydrophilic coating layer formed on at least a portion of the surface of the base body,
wherein the organic hydrophilic coating layer comprises the following components (A), (B) and (C):
(A) at least one chitosan compound selected from the group consisting of chitosan and derivatives thereof;
(B) at least one carboxylic compound having at least two carboxyl groups per molecule thereof; and
(C) at least one hydrophilic polymeric substance different from the above-mentioned compounds for the components (A) and (B),
the components (A) and (B) in the organic hydrophilic coating layer being present in a total solid content of 20% by mass or more, and
the component (C) in the organic hydrophilic coating layer being present in a solid content of 0.1 to 10% by mass.
In the aluminum alloy heat exchanger of the present invention, the chitosan derivatives for the component (A) are preferably selected from glycerylated chitosans.
In the aluminum alloy heat exchanger of the present invention, the carboxylic compound for the component (B) is preferably selected from the group consisting of oxalic acid, malonic acid, maleic acid, fumaric acid, succinic acid, malic acid, citric acid, tartaric acid, phthalic acid, itaconic acid, mellitic acid, trimellitic acid, trimesic acid, pyromellitic acid, naphthalenetetracarboxylic acid, propanedicarboxylic acid, butanedicarboxylic acid, pentanedicarboxylic acid, hexanedicarboxylic acid, heptanedicarboxylic acid, butanetricarboxylic acid, butanetetracarboxylic acid, cyclohexanetetracarboxylic acid, hexanetricarboxylic acid, acrylic acid polymers, methacrylic acid polymers and acrylic acid-methacrylic acid copolymers.
In the aluminum alloy heat exchanger of the present invention, the component (A) and the component (B) are preferably present in a solid mass ratio (A):(B) in the range of from 3:1 to 1:3, in the organic hydrophilic coating layer.
In the aluminum alloy heat exchanger of the present invention, the component (C) is present in a solid content of 0.1 to 5% by mass, in the organic hydrophilic coating layer.
In the aluminum alloy heat exchanger of the present invention, the hydrophilic polymeric substance for the component (C) is preferably selected from the group consisting of natural proteins, alginate salts, starch and modification products thereof, cellulose compounds, vinyl acetate polymers and copolymers and saponification products thereof, alkyleneoxide polymers and copolymers, water-soluble polyester resins, (meth)acrylamide resins, N-vinyl carboxylic acid amide resins, water-soluble polyamide resins, (meth)arylic copolymer resins, saponification products of acrylonitrile polymers, hydroxyethyl (meth)acrylate resins, vinyl pyrrolidone resins and cross-linking products of the above-mentioned polymeric substances.
The aluminum alloy heat exchanger of the present invention optionally further comprises an undercoat layer formed between the surface of the base body of the aluminum alloy heat exchanger and the organic hydrophilic coating layer and comprising at least one member selected from chromate compounds, zirconium compounds, titanium compounds and organic coating materials.